SOLVING ADHESION AND DIE BUILDUP PROBLEMS IN EXTRUSION COATING Bruce Foster Mica Corporation ABSTRACT Poor adhesion and die buildup are common problems in the extrusion coating industry. In the case of polymer systems requiring stabilization packages (e.g.: polypropylenes, linear-low density polyethylenes, and metallocene grades), such problems can sometimes be caused by a mismatch between the resin supplier’s stabilization package and the customers’ needs. This paper, based on “real-life” examples, shows how a simple lab test -oxidative induction behavior -can be used to optimize additive packages to solve such problems. BACKGROUND In all extrusion coating processes, polymers are oxidized to some extent as they go from pellet to coating. In most cases, sufficient oxidation of the melt curtain in the air gap is necessary to effect good adhesion. On the other hand, excessive oxidation during extrusion can result in a buildup of oxidized polymer in the extruder, on the screen pack, and at the die-lips, resulting in streaks or die-lines. Thus, an analytical tool to correlate the oxidative stability of a resin with end-use performance can be an important tool in the development of new or improved resins for extrusion coating. In this paper, we use several product development success stories to illustrate the merits of such a tool-oxidative induction testing. EXPERIMENTAL For this work, a Perkin-Elmer DSC-7 differential scanning calorimeter was used, although any similar instrument, when equipped with a gas switching accessory, should be suitable. Also needed are supplies of pure nitrogen and oxygen and a means of regulating and measuring the gas flow rates. The instrument used in this study is shown schematically in Figure 1. The test method used is in accordance with ASTM D3895, and is summarized as follows:

1. A 10 mg. sample is placed in an open test pan.

2. Heat to 200°C (30°C/minute heat rate) with nitrogen purging.

3. Hold at 200°C (i.e. isotherm) for 5 minutes.

4. Switch to oxygen purge at a gas flow rate of 10 cc/min. The effect then, is to induce oxidation of the exposed polymer surface, which occurs once its limit of resistance to oxidation is reached. Because the oxidation reaction is exothermic, it is easily detected on the test thermogram, as illustrated in Figure 2. The time between switching to oxygen and the extrapolated onset of the exotherm is defined as the polymer’s oxidative induction time. (See figure 2) The effect of temperature on the induction times is rather dramatic, as illustrated in Figure 3. For our purposes in this work, 200°C was determined to give a good balance between induction times long enough to get a good baseline, yet short enough to keep the test time reasonable. EXAMPLES The following examples demonstrate use of this method to solve stability-related problems. EXAMPLE 1: Problem: Poor adhesion

In a commercial extrusion coating operation, Formula A was observed to have poor adhesion to a paper substrate, whereas Formula B exhibited good adhesion. Testing revealed A had a longer oxidative induction time, as illustrated in figure 4. The stabilization package in A was changed to reduce this time from 13 minutes to ~2 minutes, as illustrated in Figure 5. This revised formulation, A’ gave excellent adhesion. EXAMPLE 2: Problem: Die buildup A second commercial extrusion coating operation, very similar to that discussed above, was using Product C to successfully coat paper in an application requiring a very uniform coating profile. When Product D (a more desirable polymer for economic reasons) was substituted, the process was plagued by die buildup, resulting in die streaks on the coating. Figure 6 shows that Product D had a shorter oxidation time than C, suggesting that degradation in the extruder was causing the problem. When the stabilization package in D was adjusted to improve the oxidation resistance (Formulation D’), as illustrated in figure 7, the die buildup problem was resolved. Figure 7 also illustrates the importance of comparing not only the extrapolated onset, but the slope of the oxidation exotherm. Although the visible onset of oxidation for D’ is earlier than that of C, the lesser slope for D’ suggests it oxidizes at a slower rate than C, and the result is a product that adequately survives the extrusion process. CONCLUSION These examples illustrate the utility of oxidative induction testing for solving polymer stability problems, such as adhesion and die buildup. They also demonstrate the reality that different extrusion operations, although they may be performing similar functions, can have significantly different stability needs. Careful use of this method can successfully pinpoint the additive requirements for meeting these needs.

2007 PLACE Conference

September 16-20

St Louis, MO

Solving Adhesion and Solving Adhesion and Die Buildup Problems Die Buildup Problems in Extrusion Coatingin Extrusion Coating

Bruce FosterTechnical Sales Mgr.Mica Corporation

OutlineOutline

•• Background defining need for a methodBackground defining need for a method

•• Description of experimental setDescription of experimental set--upup

•• Examples of method utilityExamples of method utility

•• Summary / ConclusionSummary / Conclusion

Background Defining NeedBackground Defining Need

•• Extrusion coating resins requiring stabilization:Extrusion coating resins requiring stabilization:

–– HighHigh--Density PolyethyleneDensity Polyethylene

–– MediumMedium--Density PolyethyleneDensity Polyethylene

–– LinearLinear--low Polyethyleneslow Polyethylenes

–– Metallocene PolyethylenesMetallocene Polyethylenes

–– PolypropylenesPolypropylenes

Background Defining NeedBackground Defining Need

•• Stabilization Package Affects:Stabilization Package Affects:

–– Oxidation / degradation in the extruder Oxidation / degradation in the extruder

(influence die buildup)(influence die buildup)

–– Oxidation in the airOxidation in the air--gap (influences adhesion)gap (influences adhesion)

Background Defining NeedBackground Defining Need

•• Lab Method to Measure Effects of Various Lab Method to Measure Effects of Various

Stabilization Packages:Stabilization Packages:

Oxidative Induction TimeOxidative Induction Time

ExperimentalExperimental

•• Oxidative Induction Time SetupOxidative Induction Time Setup

•• Test ConditionsTest Conditions

Experimental SetupExperimental Setup

Experimental ConditionsExperimental Conditions

Conditions Conditions –– Why 200Why 200ooC ?C ?

Examples of UsefulnessExamples of Usefulness

•• Example 1 Example 1 –– Solving Adhesion ProblemSolving Adhesion Problem

•• Example 2 Example 2 –– Solving Die Buildup ProblemSolving Die Buildup Problem

Example 1 Example 1 –– Adhesion ProblemAdhesion Problem

Example 1 Example 1 –– Adhesion SolutionAdhesion Solution

Example 2 Example 2 –– Die Buildup ProblemDie Buildup Problem

Example 2 Example 2 –– Die Buildup SolutionDie Buildup Solution

OutlineOutline

•• Background defining need for a methodBackground defining need for a method

•• Description of experimental setDescription of experimental set--upup

•• Examples of method utilityExamples of method utility

•• Summary / ConclusionSummary / Conclusion

Summary / ConclusionsSummary / Conclusions

•• Examples demonstrate oxidative induction Examples demonstrate oxidative induction test can be used to define resins with:test can be used to define resins with:

–– Predictable Adhesion Performance, andPredictable Adhesion Performance, and

–– Acceptable Die Buildup ResistanceAcceptable Die Buildup Resistance

Secondary ConclusionSecondary Conclusion

•• No acronyms used in this manuscript or No acronyms used in this manuscript or presentation!presentation!

•• Join Join ““STAAFSTAAF”” ––““Society To Abolish Acronyms ForeverSociety To Abolish Acronyms Forever””

Special ThanksSpecial Thanks……

•• Eastman Chemical Company Eastman Chemical Company –– for for supporting this work in the 1990supporting this work in the 1990’’ss

•• Mica Corporation Mica Corporation –– For support in this For support in this decade!decade!

Thank YouThank YouPRESENTED BY

Bruce FosterTechnical Sales Mgr.Mica Corporationbfoster@mica-corp.com

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